Structural and Colloidal Attributes of Protein Matrices Extracted from Renewable Resources and Evaluation of Their Film-Forming Capacity for Sustainable Food Packaging

Novel and renewable solid streams derived after the deshelling of Lathyrus ochrus seed (SBSD), grass pea seed (L. sativus) (GPS) and defatted sunflower seed (SFS), were used to produce protein-rich fractions and protein isolates (PI) with > 85% purity. The deconvolution of spectral signals in FTIR spectra revealed the dominance of β-structures over α-helices, as it was also verified by circular dichroism. The presence of essential amino acids in GPS PI and SBSD protein-rich fraction was confirmed by their UV–Vis fingerprint (289 nm and 293 nm). The total luminescence spectra of dry GPS PI and SFS PI showed multiple emission peaks. The pH of protein dispersions/solutions significantly affected protein solubility (up to 95%) and the size distribution as monitored by the dynamic and electrophoretic light scattering techniques. The sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) indicated complex polypeptide banding patterns with molecular weights between 13 and 94 kDa for both PIs. All protein fractions showed promising emulsion stability indices (28–33%) and enhanced capacity to withstand alterations over time. Subsequently, novel biofilms were cast using matrices of the produced protein fractions. The determination of the films solubility (35.9–46.2%), water vapor permeability (1.2–1.9 × 10⁻¹⁰ g/Pa·m·s), contact angle (77–78°), and thermal profile demonstrated their potential to be used as food packaging materials. This study proposed a circular bioeconomy approach enabling the re-entrance of agri-food residues in the food chain, enlarging the application pool of waste materials and thus making a substantial contribution towards long-term world sustainability.